Barium and neodymium isotopic anomalies in the Allende meteorite

Abstract

Isotopic anomalies have been found for Ba and N d in two inclusions from the Allende meteorite. These inclusions are typical Ca-Al-rich objects associated with early condensates from the solar nebula but have distinctive 0 and Mg isotopic anomalies of the FUN type. Sample C1 shows a depletion only in ^(135)Ba of 2 parts in 10^4 and normal Nd. Sample EK1-4-1 shows large positive excesses in the unshielded isotopes ^(135)Ba and ^(137)Ba of 13.4 and 12.3 parts in 10^4, respectively. The Nd isotopic composition in EK1-4-1 is highly aberrant in at least five isotopes. Both the Ba and Nd anomalies can be explained by a model of r-process addition. These anomalies are found to be uniform between coexisting mineral phases. These observations show the existence of substantial isotopic anomalies in refractory elements in the neighborhood of Xe and extend the range of elements showing isotopic effects to 0, Ne, Mg, Ca, Kr, Xe, Ba, and Nd. The observations, in conjunction with the presence of ^(26)Al (r_(1/2) = 7 X 10^5 years), are interpreted as the result of a nearby supernova explosion which produced elements over a wide mass range and injected them into the early solar nebula shortly before condensation.